The invention relates to a process for the preparation of 2-pyridone.
According to prior art, 2-pyridone can be prepared in the liquid phase in a three-stage process starting from pyridine. In the first stage, pyridine is converted with hydrogen peroxide practically quantitatively to pyridine-1-oxide. The reaction medium is acetic acid. The first stage is described in R. A. Abramovitch and E. M. Smith, pyridine and its derivatives, Volume 14, Supplement Part 2, Chapter 4 at page 5. In the second stage, the stage one product is converted with acetic anhydride into acetoxypyridine where in the second stage the yield is not more than 65% (see Chemical Abstracts 63: 14807 f). The final stage, a hydrolysis stage, proceeds quantitatively. See also Chemical Abstracts 63: 14807 f. The above-described process is objectionable because it is a laborious liquid-phase process and also because the starting material, pyridine, is very costly. In the second stage, conversion with acetic anhydride into acetoxypyridine, the yield is not more than 65% (see Chemical Abstracts 63: 14807 f). A hydrolysis stage as final stage proceeds quantitatively (vide also Chemical Abstracts 63: 14807 f). Such a process is objectionable because of the laboriousness of a liquid-phase process as well as the costly starting material i.e. pyridine.
According to another known process (see Japanese Patent Application No. 51143672) 2,4-hexadienamide can be converted to 2-pyridone in the presence of a palladium salt and a tertiary amine in an aprotic solvent through ring closure, with a yield of 75%. The objectionability of a liquid-phase process exists here, too. Also, the starting material, a poly-unsaturated carboxamide, is costly.
Alternatively, as described in J. Heterocyclic. Chem. 16 (1979) pages 1283 through 1286, pyridine can be oxidized in the gas phase to 2-pyridone in the presence of CuSO.sub.4.5H.sub.2 O at 300.degree. C. The selectivity of this conversion is 95% but the conversion is only 20%. This process is objectionable because high pressure equipment is required in order to conduct the conversion. In addition, this process suffers from the further defect in that it also uses the costly starting material, pyridine.